1. Mar 15, 2012

### Jarfi

I have been learning about relativity, on my own, just checked how it worked, what the main idea was, I understand the concept now, but there is a thing that I can't work out.

Say you would take a space ship from earth to the nearest galaxy, in 95% lightspeed, earth sees you as travelling faster, and they see you moving slower, so you should come back, having aged lesss than them, ok at first I got that, but than they talked about how

I could also say, that they were the ones acclerating, I see earth acclerating from me, and I'm stuck in place, or me at slowing down, So i see them having a slower passage of time, than they should have aged less wen I come back.

Who the hell aged less, I don't get it!

Last edited: Mar 15, 2012
2. Mar 15, 2012

### Janus

Staff Emeritus
Re: Confused about relativity, pls help.

No, you can't say this. You have to fire your engines in order to come to a stop and then return to Earth. The Earth didn't have to do anything in order for to meet up again. In Special Relativity, you can always know who actually accelerated.

3. Mar 15, 2012

### Jarfi

Re: Confused about relativity, pls help.

Why did I get that in one seconde because you said it?

god damnit, I gotta go get some more sleep.

But thank god, the world is looking pretty clean now, for now.

4. Mar 17, 2012

### Jarfi

Re: Confused about relativity, pls help.

Oh but what if you meet a random space ship passing by, maybe it came from billions of light years away, will it than depend on witch one if us started accelerating? maybe i and my galaxy accelerated to him or maybe he accelerated to me,

Is the thing about reletivity, that it looks to both as if they are stationary or accelerating, but only one is right?

5. Mar 17, 2012

### Staff: Mentor

Re: Confused about relativity, pls help.

If you meet only once, how do you compare how much the two of you have aged?

6. Mar 17, 2012

### Jarfi

Re: Confused about relativity, pls help.

You either look at his condition in a scope, or you both return to meet.

7. Mar 17, 2012

### ghwellsjr

No, if only one is accelerating, they both can tell which one. But if they both have stopped accelerating so that there remains a speed difference between them and they wait long enough so that they can no longer see any change in the speed of the other one, then from that point on, either one can say the other one is doing all the traveling.

EDIT: It doesn't matter if they ever meet, only that they no longer see the other one as changing their velocity.

Last edited: Mar 17, 2012